2-Methylsulphonyl-4-nitroaniline (0.66 g) was diazotized in a mixture of 3:1 v/v glacial acetic acid:propionic acid (40 ml) by adding sodium nitrite (0.21 g) in concentrated sulphuric acid (2.5 ml) dropwise at 0° C. The resulting diazonium solution was added to N-(benzotriazol-5-yl)naphth-2-amide (1.0 g) dissolved in 3:1 v/v glacial acetic acid:propionic acid (100 ml) containing ammonium acetate (16.2 g) and the mixture was stirred at room temperature for one hour. The mixture was poured onto ice and the product was filtered and crystallized in aqueous pyridine. Yield 1.16 g, m.p. 260° decomp., λmax (methanol) = 577 nm.
